Field:
Embodiments of the invention generally relate to wireless communications networks, such as, but not limited to, the Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (UTRAN), Long Term Evolution (LTE) Evolved UTRAN (E-UTRAN), LTE-Advanced (LTE-A) and/or future 5G radio access technology. Certain embodiments may relate to device-to-device (D2D) communication integrated into such communications networks.
Description of the Related Art:
Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (UTRAN) refers to a communications network including base stations, or Node-Bs, and radio network controllers (RNC). UTRAN allows for connectivity between the user equipment (UE) and the core network. The RNC provides control functionalities for one or more Node Bs. The RNC and its corresponding Node Bs are called the Radio Network Subsystem (RNS).
Long Term Evolution (LTE) refers to improvements of the UMTS through improved efficiency and services, lower costs, and use of new spectrum opportunities. In particular, LTE is a 3rd Generation Partnership Project (3GPP) standard that provides for uplink peak rates of at least 50 megabits per second (Mbps) and downlink peak rates of at least 100 Mbps. LTE supports scalable carrier bandwidths from 20 MHz down to 1.4 MHz and supports both Frequency Division Duplexing (FDD) and Time Division Duplexing (TDD).
Two types of communication networks include cellular networks and ad-hoc networks. As discussed above, a cellular network (e.g., UTRAN) is a radio network made up of one or more cells, where each cell is served by at least one centralized controller, such as a base station (BS), a Node B or eNB. In a cellular network, the UE communicates with another UE via the centralized controller, where the centralized controller relays messages sent by a first UE to a second UE, and viceversa. In contrast, in an ad-hoc network, a UE directly communicates with another UE, without the need of a centralized controller. Utilizing a cellular network versus an ad-hoc network has its benefits and drawbacks. For example, utilizing a cellular network over an ad-hoc network provides the benefit of easy physical resource control and interference control. However, utilizing a cellular network over an ad-hoc network also provides the drawback of inefficient physical resource utilization. For instance, additional physical resources may be required in a cellular network when the two UEs are close to each other, as compared to an ad-hoc network.
A hybrid network utilizes both a cellular mode and a device-to-device (D2D) transmission mode. In a hybrid network, a UE may choose or be ordered to communicate either via a cellular mode or a D2D transmission mode. As an example, a hybrid network may allow UEs to communicate either via a cellular mode (i.e., via a centralized controller) or via a D2D transmission mode where the UEs may establish a direct channel which may or may not be under the control of a centralized controller. Thus, a hybrid network may improve total system performance over a cellular network or an ad-hoc network. However, in order to utilize a hybrid network, issues related to physical resource sharing and interference situations may need to be addressed.
In addition, proximity services (ProSe)/D2D discovery and communication is one of the ongoing study items for 3GPP Release 12 (Rel-12) standardization (as well as Release 13 and beyond). D2D scenarios that are currently being studied in 3GPP include D2D in network coverage, out of network coverage, and partial network coverage scenarios.